Which of the following is not a producer?
1. Spirogyra
2. Agaricus
3. Volvox
4. Nostoc

Options

A. Spirogyra
B. Spirogyra
C. Agaricus
D. Nostoc

Explanation

To determine which of the following organisms is not a producer, we need to understand the definition of a producer in an ecosystem. A producer is an organism that can produce its own food, typically through the process of photosynthesis, which requires chlorophyll.

Let's analyze each option step by step:

1. **Spirogyra**:
- Spirogyra is a type of green algae.
- It contains chlorophyll, which allows it to perform photosynthesis.
- Therefore, Spirogyra is a producer.

2. **Agaricus**:
- Agaricus is a genus of fungi, commonly known as mushrooms.
- Fungi do not contain chlorophyll and cannot perform photosynthesis.
- As a result, Agaricus cannot produce its own food and is not a producer.

3. **Volvox**:
- Volvox is a green algae that forms spherical colonies.
- It contains chlorophyll and is capable of photosynthesis.
- Therefore, Volvox is a producer.

4. **Nostoc**:
- Nostoc is a type of blue-green algae (cyanobacteria).
- It also contains chlorophyll and can perform photosynthesis.
- Thus, Nostoc is a producer.

After analyzing all the options, we conclude that the only organism that is not a producer is **Agaricus**.

**Final Answer**: Option 2 - Agaricus is not a producer.